M1911 hit the nail right on the head: you don't have backup on the way; you don't wear body armor (at least, most of us don't); you won't have investigating officers that will be sympathetic to you (they would be for one of their own); if you get wounded or killed, you won't have the city or the victim paying for medical bills or funeral expenses, or taking care of your family; no one but you will be paying your legal expenses, which will be from both criminal and civil charges; regardless of how "right" you think your actions were, you have to defend your actions in court, and depending on where you live and what the law is, you may be subject to surrendering all your firearms to police until the criminal charge is dismissed.
The point of carrying is to defend yourself and loved ones. It's not a piece of jewelry to show off during a shoot out. It's not a guarantee that you will prevail in a dangerous situation. It's a tool of last resort, as in you either use it or you die. As Florida's guide to concealed carry puts it, "carrying a gun does not make you a good samaritan or a freelance policeman."
Bottom line, if you're not prepared to accept the consequences, then reconsider the decision to carry a firearm.
You want to help someone in danger? Use your cellphone to call police; observe what's going on and take pictures/video (if your cellphone is so equipped) and/or notes. Be a good witness.
I'm not afraid of the guy who wants many guns; I'm afraid of the guy who wants just one.